Methods of molding powders of metal character



Patented Apr. 22, 1952 METHODS OF MOLDING POWDERS OF METAL CHARACTER ,Eugene Wainer, Clevelan signor, by mesne assi Products, Inc.,

d Heights, Ohio, as-

gnments, to Thompson Cleveland, Ohio, a corporation of Ohio No Drawing. Application March 1, 1949, Serial No. 79,109

6 Claims.

In the field of powder metallurgy, it is well 'known to form articles by feeding a metered amount of metal powder into a die cavity and applying high pressure to initially consolidate, and then the formed piece is fired or sintered in a controlled atmosphere at temperatures re quired to obtain a desired density.

The advantages and possibilities inherent in use of powder metallurgy are well recognized commercially, but, at present, there are serious limitations in the available practices. For example, in view of the fact that the piece is formed in a die by pressure, the size and shape of the articles that can be prepared is restricted. Thus, the sizes must be relatively small and the shapes not too complicated. In addition, the pressure cannot be applied equally in all directions due to die design limitations with the result that density difierences are encountered in the article, which lead to distortion or lack of dimensional uniformity. Compensation for the difierences in density of small articles is possible through die design, but such compensation becomes increasingly diflicult as the size of the piece or the thickness thereof increases. Wires, long rods, I, U, X, and Y beams, tubes, slotted tubes, honeycomb tubes, bars, and the like, for instance, cannot be made in any great length from powdered metals in a single forming operation by the techniques now available in powder metallurgy. When such products are desired, secondary or complicated forming procedures are required. For this reason, metals which can be formed only by powder metallurgy are not available commercially in the form of tubes or articles of great length unless working is possible after the sintering fire. Metals which are hot-short or brittle and cannot be worked for these reasons eliminate the possibility of forming wires and tubes of undetermined length entirely. Such materials are chromium, the high chromium alloys, beryllium and the like. This inherent property of chromiumfor example has limited the amount of chromium which may be present in the high resistance conductors used when electricity is employed as the source of heat. In the jet aircraft industry, alloys containing high percentages of chromium would be useful for turbine buckets and tail pipes if suitable methods of forming were available. In the case of both chromium and beryllium and metals like titanium, zircon, boron, silicon, germanium and the like, the inherent difficulties in working these metals and their alloys which contain on the order of 50% or more has prevented commercial utilization to the extent possible with other metals or alloys. For example, germanium is a-highly useful material in rectifier application. Its brittleness is so great, however, that wires are not available due to the inability for working and drawing.

In accordance with the present invention, however, powders of metal character may be brought into desired shape without the limitations which have heretofore prevailed in powder metallurgy. Thus, articles may be prepared in forms not previously possible by powder metallurgy.

It is then,'an object of the invention to provide a method of preparing from metal powders articles of any desired length having a uniform density throughout and characterized by a cross section of constant form or shape.

A further object of the invention is to provide a method of preparing from metal powders, articles having a uniform density throughout and characterized by an un-uniform cross-section and shapes of varying dimensions.

A still further object is to provide a, novel plastic mass and its method of preparation, from which the novel articles of the present invention may be produced.

A still further object is to provide a novel plastic mass and its method of preparation, said plastic mass being so constituted that similar reactions develop in the sintering process which add cementation and sintering.

Other objects, including the provision of a group of compositions from which the metalarticles described herein may be prepared, will be apparent from a consideration of this specification.

In accordance with the present invention, av

plastic mass is formed from a metallic powder by use of a resin which is thermoplastic in nature and an oily material solid at room tem-. perature and liquid at temperaturesof formation. This oily material is not a solvent or" resins, or other thermoplastic material as described. These are present in amounts sufficient to provide a ratio of relative volume between metal powder and resin of at least 65 to 35 and preferably up to 5,0 to 50. The said mass is heated to a temperature sufiicient to melt the wax ingredient, but below the temperature of which any distillation or destruction of the wax takes place, and the plastic mass is then extruded either through a die corresponding in cross section to the cross section desired in the article or to a mold corresponding to the shape desired. The formed article is then sintered under conditions of temperature and atmosphere imposed by the nature of the material. It is a feature of this invention that the materials will distill completely without residue or deposits of carbon in the subsequent sintering operation. It is a further feature of this invention that certain of these resinoid materials which are effective are of aid in providing eementation in the sintering operation. It is a further v.fiiaiiure of this invention that the prime base resin used as a permanently green strength binder is insoluble and in in the wax 0. m: parable additive, even though the temperature of the system is such that the wax is a liquid.

B the pres nt invent on, i is possible to extrude or injection-mold articles from. metallic powders whose green densities are comparable to the density obtained by pressure methods. Further by the present invention, it is possible to produce in a single forming operation metal articles of any length with assurance that the cross section of the article will be constant and uniform throughout the length and that the ar-. ticle will be of uniform density throughout. Many of the products which can be made by the process are articles which have not previously been produced because they are of a shape or form that cannot be obtained by the powder metallurgical procedure now available. In addition, wires with perfectly round section and having a diameter from a few thousandths of an inch up to several inches in thickness can be readily formed without, the necessity of repeated drawing or other operations. If desired, the wires can be wound in coils or repeating hairpin shapes as part of the forming operation. Furthermore, articles such as tubes, rods, I, U, X, and Y beams, slotted tubes, tubes with serrated outlines, honeycomb tubes, long gear shapes, and the like can easily be prepared. Moreover, by extruding the plastic matter into molds, a wide variety of shapes may be prepared. As an example, my novel procedures may be advantageously applied to the preparation of buckets and supercharger parts for use in jet aircraft. Herein the terms extrusion and extruding are used to refer both to extrusion through a die corresponding to the cross section desired as well as to extrusion into a mold corresponding to the desired shape. When relatively small articles or pieces are desired, these maybev readily obtained merely by crosscutting a longer piece. Furthermore, in view of the inherent nature of the process, articles of relatively large mass of bulk can be produced with greatly reduced die costs and a greatly increased rate of production as compared to conventional procedures.

Moreover, because of the nature of the materials, and the resins used, these are eliminated completely as such from the product before or during the sintering step and the endproduch- 4 therefore, does not contain any contaminant provided by the resin. In other words, these resinoid materials distill or are dissipated completely from the system without leaving residue or depositing carbon. The products of the invention are extruded articles consisting essentially of material in which the metallic crystals are non-distorted or non-elongated in contrast to the type of articles which are formed by working.

The metal powder employed with the resin systems in the preparation of the plastic mass may be prepared from any metal which is stable, in the atmosphere and is reducible to powdered form. .Metal alloys, as well as relatively pure metals, may be employed and obviously both a metal and an alloy or a plurality of metals or of alloys or a plurality of metals and alloys may be used. The choice of the metallic powder will, of course, depend on the nature of the product to be produced and the properties desired therein. Examples of materials of metal character that are applicable for use are: iron, cobalt, nickel, chromium, titanium, zirconium, manganese, copper, aluminum, lead, silicon, molybdenum, tungsten, zinc, tin, beryllium, and magnesium and alloys containing two or more thereof, for instance, brass, bronze, monel metal, stainless steel, and the like. The metals or alloys may contain the usual small percentage of non-metallic impurities or additives and at times it may be desirable to add to the metallic powder, powdered inorganic, non-metallic material in small amounts, to impart special properties to the metal product. Even in. such cases, the final product will consist essentially of metal.

Cases where additives are deliberately used are in the fields of tungsten or molybdenum, where a small amount of certain oxides are incorporated in a mass to prevent subsequent growth when tungsten is used as a lamp filament. In the case of certain alloy compositions, titanium hydride may be a common addition to aid in developing a sound material.

The particle size of the metal powder may vary over a wide range, and particle sizes ranging between mesh and a fineness of several hundred mesh can be handled readily in the process. Particles consisting of 300 mesh plus the fines normally present as the result of the milling are most easily handled and hence this range of particle size is generally preferred. In some cases, however, where low shrinkage in firing is desired, a mixture of coarse and fine particles is used-for example, 50 to '70 parts of minus 80 mesh plus 50 to 30 parts of minus 300 mesh powder. As is usual in powder metallurgy, variously sized metal powders may be used in combination to achieve special results.

As pointed out above, the powder metallic material is converted into a plastic mass which is extrudable under pressure by use of heat-fugitive materials which promote flowage. These materials are all organic in nature and it is necessary that all of them be capable of dissipation completely through a rise in temperature. It is a further necessity that any wax agent added not be a solvent or a swelling agent for the resins. A second class of resins which is important in the specification are those containing halogens. The peculiar advantages of these halogenated resins are that they distill without residue, but in distillationthey decompose so that one of the products of decomposition is a pure hydrogen halide.

This hydrogen halide is effective in improving cementation of the metal during sintering through improvement of difi'usion processes by development of a metal containing vapor phase.

Where added material of wax character is employed, this is a hydrocarbon wax which may or may not be of microcrystalline structure. Hydrocarbon waxes commonly are prepared from war; distillates in the petroleum industry, and include parafiins of crystalline character, also of amorphous nature. Through the whole range of these, the characteristic is that employed in the present connection they are fluent at molding temperatures and add slippage Or flowage property, and after the article is molded, the wax component is distilled cleanly out in the'sintering heating. .It will of course be understood that it is not necessary in all cases to use wax additives, since the thermoplastic resins themselves act effectively. The base resins useful for my purpose in the first instance are of the class identified by the generic term polymerized-monoolefinic compounds and polymerized-monoethylenically unsaturated compounds. Of particular importance in this group are resins such as polybutene, polystyrene, polyacrylate, polymethacrylate, polyethylene, polypropylene, polyvinylbutyl ether. Two of the members listed above have universal application for the purposes of my invention and the remainder are somewhat restricted in application. The two most useful resins are polybutene and polyvinylbutyl ether for all purposes. The prime reason for the distinction is that both these latter materials depolymerize and distill without residue of any kind at a temperature low enough so that no carbonization of the material results, this distillation being equally effective in both oxidizing and reducing atmospheres. The remaining resinoid materials require somewhat higher temperatures for the development of the decomposition into gaseous constituents. With metals which form carbides at low temperatures, there is some danger in these cases of the formation of a small amount of such carbides in the material using the restricted group. For this reason polybutene and polyvinylbutyl ether are the primary recommended materials and the remainder are of secondary importance with some metals. Included also with the foregoing are halogenated derivatives. These may be substituted for or used in conjunction with the aforementioned synthetic resins. These materials also decompose completely without residue, but have another property of equal importance. They are halogenated derivatives and one of the products of decomposition is a dry hydrogen halide. The advantage of the presence of this small amount of HCl is that it aids in sintering and development of dense material through acceleration of diffusion processes at the sintering temperature. Examples ofthese' classes of resins are the following: chlorinated polyethylene, fiuorinated polyethylene, chlorfluorinated polyethylene, the chlorinated diphenyls (these latter materials are commercially known as the aroclors"). These chlorinated diphenyls are available in molecular weight such that the-product varies from thin liquid to stiff resinoid solid. Derivatives are thermoplastic and the low molecular weight type act as lubricants.

In effect, the first group of resins alone or com-v binations of the first group plus the halogenatedtype constitute the base resins used in thesemixtures. The waxes which are efiective in my invention are, as stated-the high molecular weight hydrocarbons. These high molecular weight hydrocarbons melt at elevated temperatures to oily liquids and are not solvents or swelling agents for the-listed resins. In some instances, one of the halogenated resins can be used as a lubricant also. Also effective in this regard are the liquid polybutenes, that is polybutenes having molecular weights less than 1000. The molecular weight of the polyolefinic synthetic resins may vary somewhat, but aside from the liquid usage just mentioned, they may range in general about 20,000 to 200,000.

Y In the practice of my invention, I find it desirable to prepare the batch by one of two methods.

1. The resinwax system is dissolved completely in a solvent. The proper amount of metal powder is added and a thorough mix obtained. The solventis then eliminated by heating for a sum-- cientperiod at a temperature above the boiling point of said solvent.

tion into the die cavity.

2. The second procedure eliminates the use of solvents entirely. The proper amount of metal powder resin and wax is placed in a hot mixer and the batch is kneaded to a homogeneous consistency at an elevated temperature.

Once the batch is prepared, it is worked for a substantial period of time in suitable equipment while the batch is in the plastic stage. It is then transferred to a slugging machine. A slug is formed of shape such that it will fit the, barrel of the extrusion equipment.

if desired.

Where solvents are employed, these, capable pared. After the plastic mass has been extruded,-

the shaped forms are dried and sintered under conditions of temperature and atmosphere dictated by the nature of the material with one exception. During the period at which the resinoid and wax binders are distilling off, the temperature of the batch is maintained constant in the distillation range until all the organic material has been eliminated.

For proper operation of the die in the extrusion or die molding, it is desirable that the temperature be maintained sufi'iciently high to take'account of the nature of the additive material. Thus, where hydrocarbon wax is present,

the temperature should be adequately above the melting point thereof, and similarly with other additives. In general, it is desirable to maintain the temperature of the die at to 200 C.

The temperature in the sintering furnace eliminates the fugitive material added to the metal powder, vaporizing it completely out. The, sintering temperature in any given case will de-.

pendsomewhat on the particular metal being sintered, and in general may be 20 F. to several hundred degrees below the melting point.

After all the solvent is. eliminated, the batch is then ready for introduc- A vacuum de-airingprocess may be applied in the slugging operation Thus, in general, the metal powder mass is prepared by hot mixing or by evaporation from solution. The maximum ratio of metal powder volume to resinoid lubricant system volume is 65 to 35 and ratios less than this can be advantageously used. It should be noted that when these ratios are transferred to weight ratios, depending on the relative specific gravity, the relative proportion of metal resin system will vary between 90 parts of metal by weight and parts of resins by weight and 80 of metal by weight plus 20 parts of resin system by weight. When wax is added, it will consist of 5 to 35 per cent of the total resin system. The following examples are illustrative of the invention:

1. The metal powder used has a particle size of 300 mesh plus the fines resulting from grinding. The metal powder has a direct specific gravity between 7 and 9. Such metal powder may be iron, cobalt, nickel, copper, brass, bronze, stainless steel, manganese, nickel-chromium alloys, iron-chromium alloys, high iron content alloys and the like. Polybutene having a molecular weight of 60,000 is dissolved in xylene so that 9, solution results. A hydrocarbon wax is added to the polybutene solution so that the solution is equivalent to a 1% solution with respect to the Wax. The raw batch is prepared by mixing 100 grams of the respective metal powders with 80 grams of the polybutene wax solution. After thorough mixing, the batch is evaporated to dryness at 160 C. for two hours, this being suflicient to eliminate all xylene. It will be noted that the weight ratios resulting are approximately equivalent to 100 parts of material, about 8 parts of polybutene, and about 0.8 parts of wax. The xylene-free mass is kneaded in a hot mixer until smooth and is then slugged in a vacuum de-airing machine. The Slug is placed in the barrel of an extrusion press which is maintained at a temperature of about 160 C., that is, the extrusion orifice is kept hot. The mass is formed using extrusion pressure of at least 10,000 pounds per square inch and preferably as high as 20,000 pounds per square inch. The result ing shapes are transferred to furnaces and sintered under conditions of temperature and atmosphere dictated by the metal component of the shaped article, which requirements are wellknown in the powder metallurgy field.

'2. If a firing shrinkage of the order of one-half of the one obtained in Example 1 is desired, the particle size of the metal powder used is varied as follows: 60 parts by weight of 80 to 100 mesh metal powder are mixed with 40 parts by weight of 300 mesh powder. The procedure set forth in Example 1 is then followed.

3. 100 grams of metal powder according to Example 1 is placed in the receptacle of 'a .hot kneading mixer along with 10 grams of polybutene having a molecular weight of 60,000 and 1 gram of wax. The material is kneaded into a homogeneous mass at temperatures of 160 to 175 C. It is advantageous to use hot rolls subsequent to the kneading operation to insure elimination of dry spots.

4. Using the mixture of Example 2, the procedure according to Example 3 is followed.

5. In this example, the same methods and procedures described above in connection with Example 1 are employed, but the powdered metals have different specific gravities. For these reasons, to obtain optimum results, the amounts of resins and wax are modified as compared to those;

shown as follows:

- 10% Specific K Metal Polybutene Wax Gravity Solution Zirconium 6. 4 103 l. 0 Zinc 7. 14 92 0. 9 Chromium. 0. 9 96 1. 0 Molybdenu 10. 2 64. 5 0. 7 Tungsten 19.3 34 0.4 Titanium... 4. 5 146 1.5 Aluminum 2. 7 244 2. 5 Silicon. 2.0 330 3.3 Beryllium" 1.85 350 3. 5 Germanium 5. 35 121 l. 2 Boron 2. 3 282 2.8

6. The procedures in accordance with Examples 1 to 5 are followed except that polyvinylbutyl ether is substituted for the polybutene.

7. The procedure according to Examples 1 to 5 is followed except that the resinoid mass per grams of materials consists of 10 grams of polybutene and 2 grams of a chlorinated diphenyl liquid having a distillation range between 365 and 390 C. No wax is used. This chlorinated diphenyl is a light yellow viscous liquid and the commercial product Aroclor 1254 may be used.

8. The procedures according to Examples 1 to 5 are followed except that the resinoid mass per 100 grams of powder consists of 4 grams of polyhutene, 4 grams of a chlorinated diphenyl having a softening point at to C. and 2 grams of a chlorinated diphenyl which is liquid at room temperature. As the solid chlorinated diphenyl, the commercial product Aroclor 1268 and the liquid chlorinated diphenyl by the trade name Aroclor 1254 may be used. No wax is used in this example.

9. The procedures in accordance with Example 2 are used except that the resinoid mix consists of 5 grams of polybutene, 3 grams of chlorinated polyethylene and 2 grams of wax per 100 grams of metal.

10. The procedures in accordance with Example 2 are used except that 5 grams of polybutene plus 3 grams of fluorinated-chlorinated polyethylene and 2 grams of wax are used per 100 grams of metal.

'11. The procedures in accordance with Example 1 are used except that 12 grams of a chlorinated diphenyl having a molecular weight such that its softening point is 135 to 160 C. are used. No wax or polybutene is necessary here. This chlorinated diphenyl may be the trade product Aroclor 1268.

12. The procedure in accordance with Example 2 is used except that 12 grams of chlorinated polyethylene is used as the resinoid.

13. The procedures in accordance with Example 1 is used except that 12 grams of the fusi ble chlorinated diphenyl as in Example 11 is dissolved in 70 cc. xylene. No polybutene or wax is required.

14. Polybutene having a molecular weight of 60,000 is dissolved in xylene so that a 10% solution results. A hydrocarbon mineral wax having a melting point of 120 C. is added to the polybutene solution so that the solution is equivalent to a 1% solution with respect to the wax. Said mineral waxes are trade-designated as Microcrystalline. The various metal powders can be had in finenesses equivalent to 300 mesh plus the fines developed by grinding. Powders such as tungsten, molybdenum, and germanium are obtained in the proper fineness directly'by hydrogen reduction of the oxides.

Mzzcmy and firmy data.

Per Cent Sintering Sintenn Polybutene Wax per Tempera- 5 Metal 3328 2 Solution per 100 gms. ture gii y 100 grams of metal min. to 1 i? 0 metal hour mus I About F. About F. Z rconium 6. 4 103 1. 0 2, 800 2, 400 Zinc 7. 14 92 0. 9 820 750 6. 9 96 1. 0 2, 900 2, 850 10. 2 64. 5 0. 7 4, 000 3, 500 19. 3 34. 0 0. 4 5, 000 4, 000 4. 5 146. 0 1. 5 2, 800 2, 400 2. 7 244. 0 2. 5 1, 200 1, 100 2. 0 330. 0 3. 3 2, 500 2, 350 1. 85 350. O 3. 5 2, 320 2, 250 5. 12]. 0 1. 2 1, 700 1, 600 2. 3 282. 0 2. 8 3, 600 3, 000 7. 86 84. 0 0. 8 2, 600 2, 400 8. 9 74. 0 0. 7 2, 600 2, 400 8. 9 74. 0 U. 7 2, 550 2, 300 Copper 8. 92 75. 0 0. 8 l, 950 1, 550 l8-8 stainless steeL 8. 1 82. 0 0. 8 2, 550 2, 400 80Nl-20Cr 8. 2 82. 0 0. 8 2, 400 2, 300

100 grams of each of the metal powders are mixed with the amount of polybutene solution and wax indicated in the foregoing table, and after thorough mixing the xylene is eliminated by heating at 160 C. for two hours. Thexylenefree mass is kneaded in a hot mixer until smooth and then slugged in a vacuum de-airingma chine. The slug is placed in the barrel of a hot extrusion press which is maintained at a ing an extrusion pressure of 20,000 pounds per square inch.

The resulting shapes are fired in pure hydroen, and each shape is placed in a setter sand of pure alumina. 3

The hydrogen is purified as follows:, Water vapor is removed by passage .of the hydrogen through phosphorous pentoxide; oxygen is removed by passage through copper turnings heated to 1600 F.; nitrogen isremoved by passage 40 over titanium hydride heated to 2000" F.

The various metals are fired as follows: For temperatures of sintering up to 2700 F., a mullite tube furnace heated with silicon carbide resistors is used. For sintering temperatures up to 35O0 F., a molybdenum wound resistor furnace is used, the molybdenum windings being maintained in a pure hydrogen atmosphere. For temperatures above 3500 F., that is, for metals such as tungsten, molybdenum, and boron, the piece is first sintered in the molybdenum wound furnace, cooled and removed to a device where the pieces are internally fired. In this device, the required temperature is obtained by passing a current through the specimen itself, the specimen being maintained with suitable holders in a pure hydrogen atmosphere. In this way, any temperature up to the melting point of the specific sample may be obtained.

When a relatively fine grained metal is desired,

a relatively short high temperature fire is used. When coarse grained metal is desired, lower sintering temperatures and longer firing times are used, to afford opportunity for difi'usion.

15. The same as Example 14, but using the dif- 6 ferent resins and combinations of Examples 2 to 13.

Considerable modification is possible in the se lection of metal powder, the resin, and additions,

as well as in the amounts thereof employed and in the process, without departing from the essential features of the present invention.

Other modes of applying the principle of the invention may be employed, change being made as regards the detail described, provided the featur'es stated in any of the following claims, or the equivalent of such, be employed. 1

I therefore particularly point out and distinctly claim as m invention:

1. The method of making a powdered article of controlled size and porosity which comprises admixing. from 50 to 65 parts by volume of powdered metal with 35 to 50 parts by volume of a v completely distillable heat fugitive binder comtemperature of 160 C. The mass is formed us- 30 posed of a depolymerizable polymerized-monoolefinic thermoplastic resin and a distillable hydrocarbon wax which will not dissolve or swell the resin, said binder ingredients having vaporization temperatures close to the plastic range thereof, heating the admixed mass to a temperature above C. and above the softening points of the binder ingredients but below their vaporization temperatures, extruding the thus heated mass under low pressures to form an article of desired shape, and sintering the article in a nonoxidizing atmosphere at temperatures above the vaporization temperature of the binder but below the melting .point of the metal to completely eliminate the binder without action of nascent carbon on the metal.

2. The method of making a powdered metal article of desired accurate shape and uniform porosity without exposing the metal to the action of nascent carbon which comprises admixing 50 to 65 parts by volume of powdered carbide form-- ing metal with 35 to 50 parts by volume of a thermoplastic completely distillable binder having a temperature of vaporization close to its plastic range and containing a major portion of depolymerizable polymerized-mono-olefinic resin, heating the mixture to about 100 C. to soften the binder, extruding the thus heated mass into desired article shape, and firing the article at temperatures materially above the vaporization temperature of the binder to completely vaporize the binder without pyrolytically decomposing the binder.

3. The method of making a powdered metal article of controlled size and porosity which comprises heatingto a plastic flowable stage without distillation of the bind-er therein, a mixture composed of 50 to 65 parts by volume of powdered metal and 35 to 50 parts by volume of a thermoplastic completely distillable binder containing a major portion of depolymerizable polymerizedmono-olefinic resin, extruding the thus heated flowable mass into desired article'shape, and firing the article in a non-oxidizing. atmosphere at temperatures materially above the vaporization temperature of the binder to completely vaporize the binder without pyrolytically decomposing the binder.

4. The method of making a metallic article of desired shape which comprises heating to a plastic flowable stage without distillation of the binder therein, a mixture composed of 50 to 65 parts by volume of a metallic powder and 35 to 50 parts by volume of a completely distillable binder containing a major proportion of polymerizedmono-olefinic thermoplastic resin and a thermoplastic halogenated hydrocarbon, extruding the thus heated flowable mass into the shape of an article, and sintering the article at temperatures above the vaporization temperature of the binder but below the melting point of the metal to liberate hydrogen halide gas from the binder for improving the cementation of the metal particles and to completely vaporize all of the binder without formation of a residue in the article.

5. The method of making a molybdenum article which comprises heating a mixture composed of 50 to 65 parts by volume of molybdenum powder and 35 to 50 parts by volume of a completely distillable binder containin a major portion of a polymerized-mono-olefinic thermoplastic resin and a hydrocarbon wax, continuing the heating to produce a plastic flowable mass without distillation of the binder ingredients, extruding the thus heated fiowable plastic mass into desired article shape, and sintering the article at relative- 1y high temperatures to completely vaporize the binder cleanly out of the article and to sinter the molybdenum powder without forming a residue in the article.

6. The method of making a metallic article of desired shape and porosity which comprises a'dmixing 50 to 65 parts by volume of a metal powder in an aromatic hydrocarbon solution of a completely distillable binder containing a major proportion of polymerized-mono-olefinic thermoplastic resin and constituting 35 to 50 parts by volume in relation to the metal powder, vaporizing the solvent at temperatures above the boiling point of the solvent, extruding the resulting mass 12 at temperatin'es above C. but below the vaporization temperature of the binder to form an article of the desired shape, and sintering the article at temperatures above the distillation temperature of the binder to completely vaporize all of the binder without formation of a residue in the article.

EUGENE W AINER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,988,861 Thorausch et al. Jan. 22, 1935 2,001,134 Hardy May 14, 1935 2,097,502 Southgate Nov. 2, 1937 2,162,178 Marasco et a1 June 13, 1939' 2,196,875 Sandler et a1 Apr. 9, 1940 2,199,526 McCowen May 7, 1940 2,231,160 Gottschalt Feb. 11, 1941 2,238,893 Fischer Apr. 22, 1941 2,298,846 Skooglund Oct. 13, 1942 2,339,958 Sparks Jan. 25, 1944 2,377,153 Hunter et a1 May 29, 1945 2,378,539 Dawihl June 19, 1945 2,380,126 Sturm July 19, 1945 2,386,544 Crowley Oct. 9, 1945 2,403,657 Harvey July 9, 1946 2,446,872 Ehlers Aug. 10, 1940 FOREIGN PATENTS Number Country Date 573,338 Great Britain Nov. 16, 1945 801,060 France May 11, 1936 856,495 France Mar. 23, 1940 OTHER REFERENCES lurgy, published in Modern Plastics, vol. 24, June 1947, pages 196 and 198. 

1. THE METHOD OF MAKING A POWDERED ARTICLE LOF CONTROLLED SIZE AND POROSITY WHICH COMPRISES ADMIXING FROM 50 TO 65 PARTS BY VOLUME OF POWDERED METAL WITH 35 TO 50 PARTS BY VOLUME OF A COMPLETELY DISTILLABLE HEAT FUGITIVE BINDER COMPOSED OF A DEPOLYMERIZABLE POLYMERIZED-MONOOLEFINIC THERMOPLASTIC RESIN AND A DISTILLABLE HYDROCARBON WAX WHICH WILL NOT DISSOLVE OR SWELL THE RESIN, SAID BINDER INGREDIENTS HAVING VAPORIZATION TEMPERATURES CLOSE TO THE PLASTIC RANGE THEREOF, HEATING THE ADMIXED MASS TO A TEMPERATURE ABOVE 100* C. AND ABOVE THE SOFTENING POINTS OF THE BINDER INGREDIENTS BUT BELOW THEIR VAPORIZATION TEMPERATURES, EXTRUDING THE THUS HEATED MASS UNDER LOW PRESSURES TO FORM AN ARTICLE OF DESIRED SHAPE, AND SINTERING THE ARTICLE IN A NONOXIDIZING ATMOSPHERE AT TEMPERATURE ABOVE THE VAPORIZATION TEMPERATURE OF THE BINDER BUT BELOW THE MELTING POINT OF THE METAL TO COMPLETELY ELIMINATE THE BINDER WITHOUT ACTION OF NASCENT CARBON ON THE METAL. 